differance between stock and progressive springs

I am in the process of doing my fork seals and possible going with a progressive spring but when I disassembled the forks the spring looks exactly like the ones I was going to buy. The springs in there are tighter on the top end than the bottom and have about a 6" metal tube that sits on the spring retainer. Is this the stock setup or has someone already played with them?

 

The stock springs ARE progressively-wound, just like the Progressive brand springs. The difference is that the Progressive spring rates (initial and final) are stiffer so that they work well without additional air pressure added to the forks, and the forks work better that way (longer seal life, less stiction, better response to bumps).

Edit: Whoops, I had Turbo Seca on the brain; I don't know if your bike has air forks or not.

 

Actually, original springs are not quite the same as the progressive springs:

Inner Tube Fork Springs:

Top-quality aftermarket progressively wound FRONT FORK COIL SPRINGS don't just "restore" the performance to your front forks, they actually improve it over the original equipment. Spring and suspension technology has come a long way in the 30 years since the XJ model bikes were designed and built, and our line of performance front coil springs will not only get rid of the sags and "mush" in your front end, but will give your bike a crisper, more controllable and predictable ride and handling quality due to their superior design, engineering, and manufacturing.

Original coil springs are what are known as "dual rate springs"........they have one fixed spring rate until a certain level of compression is reached, and then a firmer, stiffer rate (stronger resistance to compression) takes over (soft, soft, soft, soft, boom! stiff, stiff, stiff.......).

Replacement springs are what are known as a "progressive rate springs".........meaning that as the load on them increases, they get progressively firmer (softest, softest, soft, less soft, firm, firmer, firmer, really firm), rather than the "all or nothing" transition that takes places with the stock springs. Progressive rate springs tends to give both a smoother, less harsh ride, as well as increasing the performance of the front suspension during enthusiastic driving and the suspension action that it creates.

 

You're right, that's how they were described on paper back then. But, unless the initial coils go into actual coil bind before the secondary coils compress at all, the springs ARE truly progressive and not actually dual-rate.

At any rate ( ), it really doesn't matter. If the bike has air forks, find an appropriate progressive spring of any brand that doesn't require added air pressure.

 

That's actually not possible, all coils deform in response to the load, until they bind. You can't have some coils compress and others not compress as you describe.

Spring rate is a measure of spring deformation (distance) for a given load (force). It is determined by the geometry of the active coils. As long as the spring geometry isn't changing (diameter of the coil, wire diameter, number of active, or non-bound, coils) the rate is constant.

It's actually the coil binding that changes the spring rate. Coils bind when they basically "run into each other" and there's no room to deform. This changes the geometry.

Dual rate springs have one section that will bind all at once (all coils are deforming, but a section runs out of space before the rest). A progressive spring as Chacal described will have coils that progressively bind as load is applied, changing the rate gradually.

 

Sure you can (okay, for all practical purposes)! Think of a very light initial rate and a very heavy secondary rate. BUT, that's not how the stock "dual-rate" springs actually performed IMO. That was my point. That's why the stock springs are not true dual-rate. You need to reread my post.

Degreed (actually Mechanical/Aerospace) suspension engineer with lots of OEM suspension supplier experience here (including Metric/American motorcycles and ATVs in addition to BMW/Mercedes/Ford/Chrysler, etc. automotive suspensions). I used to produce custom valving for the Polaris race ATVs back when. If you want the benefit of some very wordy realworld suspension experience, we'll go to PMs.

 

It's not just that the Progressive BRAND springs are "progressive" they're simply better-performing than the originals; even compared to un-sagged, low-mileage original springs.

OP was just trying to figure out if he has original springs or if somebody already replaced them and/or added (additional?) preload. I can't answer that because I don't know if/what size preload spacers may have originally been fitted to the 750 Max.

 

Dcesa1 probably time to get a manual? Should be in there.

 

They are probably the original springs then if some come with stock spacers based on the condition of the bike. Yes they do have air forks but the one seal was blown and they dont have the air equalizer in them causing the forks to be super spongey. I will probably just replace the seals add 5 lbs and hopefully I will be satisfied otherwise I will rip them apart again. These are some of the easier forks I have disassembled.

 

Just replace the springs now. Less than $100 and well worth it. I replaced a set of stock springs with 7000 miles on them with Progressives. Then I took those low-mileage springs and used them to replace the completely trashed (over 1" measurable sag) springs in my 27K bike.

Once both bikes were "done" brakes rebuilt, forks rebuilt, stainless lines and drilled rotors on both, etc--- ridden back-to-back the superiority of the 2008-made Progressive Suspension springs over the stock 1980 Yammie springs is obvious. Better over bumps and tar wiggles, more solid in the corners, and better stability and traction under braking.

Worthwhile upgrade.

 

went to put my new progressive Progressive brand springs in the other day, the old springs stuck out around an inch over the top of the fork,the new springs are nearly 3 inches shorter, should i get some pipe and make it come out the top about an inch for a bit of pre load? also can some one tell me exactly how much new oil to put in after i drain out the old, this will be done with forks ,tyres still on bike, thanks in advance, ken

 

The instructions should be clear on the length of pvc pipe to place at the top for the proper pre-load.

 

On my bike the manual specs like 278cc and some say its 257cc so I'm not sure how much to add.

 

I'm pretty sure it would say on the instructions from progressive, not your bikes manual.

On the progressive site, it says to re-use the stock spacer. are you doing that?

 

The instructions with mine were very general nothing specific to xj750 and the supplied spacers didn't even come up to th caps. After a coupla trial and errors i have 85mm spacers, 295ml of 10w fork oil. Th spacers sit about an inch above th fork when dropped in, but i didn't actually measure that. Th amount of oil is 15ml less than for stock springs, i just made that up and it seems ok in use. No added air pressure. 'Static sag' -- plenty on th net about that--was what i based th spacer length on and then how it felt riding..I'm happy with th results and don't plan on any more fork fiddling.

 

I ended up replacing the seals and filling them back up with 15wt fork oil still a night and day difference from what they were. I haven't added air yet because I only have a compressor and would rather use a bike pump.

 

hmm. ill have to remember that, i'm going to put progressive springs in when i replace my head tube bearings.

thanks for the info!